It is common practice for various devices to communicate with one another using wireless data transmission. Examples of such devices include consumer electronics products, such as mobile telephones and mobile computing devices and distributed date centre networks operating to collect data in a commercial or industrial setting and report that data back to a central location. An example of such a wireless transmission system is that based on the IEEE 802.11 transmission standards, generically referred to by most consumers simply as “WiFi”. The increasing use of wireless transmission systems such as the 802.11 standards is intended to support new outdoor uses, such as smart grids, industrial process sensor networks and extended range WiFi for cellular traffic offloading, as well as the traditional indoor wireless access functions experienced by most consumers.
The traffic pattern from these applications varies significantly. For the smart grid and industrial process centres networks, the required data rates can be as low as 100 kbps and the data traffic is periodical and of small payload size, for instance 250 bits per packet. On the other hand, for extended range WiFi intended for cellular traffic offloading, the traffic may require a data rate of up to 10 Mbps with a large packet size and a very “burst” transmission pattern. For cost-efficient usage within any single wireless network, the network stations must be capable of providing these different services.
The wireless transmissions standards adopted for such systems typically require that transmission over a number of different bandwidths is supported. For example, it may be mandated that the devices conforming to the standards support reception of signals transmitted in both 1 MHz and 2 MHz bandwidths. Support for other bandwidth options may be optional. In general, the devices that have low traffic requirements, in particular small data packet sizes, by preference use narrow signal bandwidth, while high traffic stations use wide bandwidths. When the transmission channel bandwidth of the system is larger than one 1 MHz, the stations within the network may operate in different bandwidths.
One mechanism for supporting both narrow band and wide band transmission within the same transmission channel requires that the narrow bandwidth signal occupies the primary channel within the wider channel bandwidth. For mixed bandwidth operation, this results in an inefficient use of the overall spectrum and only a part of the available spectrum is utilised during narrow band transmission.